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Hmm Allwinner A1X and Exynos 4412 both have integrated Mali 400 GPUs, so there should be at least some GPU support on Linux [1].
There is an unofficial XBMC port for A1X devices which supports the HW Video Decoder of the SOC [2]. I have an A10 device at work, but unfortunately won't be in the office to play around with it for some time.
Depends on what you mean by "proper" drivers. The GPU drivers for the Raspberry Pi, like the drivers for most other development boards, consist of an open-source shim and a closed-source userspace blob [1].
HD decoding on these boards is performed using a digital signal processor (DSP) integrated into the SOC, the CPU (even with GPU support) is too slow for 1080P h264 Content. This is not specific to Android, for example TI supports use of the DSP of the Pandaboard on Linux as well [2] (it is still not very stable, at least on the OMAP 4430 version of the Pandaboard).
[1] http://airlied.livejournal.com/76383.html
[2] https://launchpad.net/~tiomap-dev/+archive/release
Edit: formatting